Electrostatic gyroscope suspension system

ABSTRACT

The invention is directed to a suspension system for an electrostatic gyroscope wherein the pulse charges applied to electrode pairs to maintain the gyroscope rotor centered between the electrodes is alternated in polarity so as to minimize the accumulated charge on the rotor.

United States Patent 15 3,697,143 Klinchuch 5] Oct. 10, 1972 [54]ELECTROSTATIC GYROSCOPE 3,221,563 12/1965 Wing ..308/l0 SUSPENSIONSYSTEM 3,262,325 7/1966 Senstad ..308/ 10 3,262,326 7/ 1966 Schott..308/10 [72] Invent Klmchuc'" Orange Cahf' 3,334,949 8/1967 Atkinson..308/10 [73] Assignee: North American Rockwell Corp'ora- 3,338,6448/1967 Atkinson et al. ..308/ 10 tion 3,619,014 11/1971 Quick ..308/l0[22] Filed: May 21, 1971 mm), Hix [21] Appl. No.: 145,679 Attomey-L. Leel-lumphries, H. Frederick l-lamann and Edward Dugas 52 US. Cl ..308/l0,74/5 [57] ABSTRACT [51] Int. Cl. ..F16c 39/06 58 Field of Search..308/l0; 74/5 The mvemw" dlrected 3 suspensw" System an electrostaticgyroscope wherein the pulse charges ap- 56 plied to electrode pairs tomaintain the gyroscope 1 References Clted rotor centered between theelectrodes is alternated in UNITED STATES PATENTS polarity so as tominimize the accumulated charge on th t 3,098,679 7/1963 De Boice..308/10 e m 3,209,602 10/1965 Biderman ..308/ 10 5 Claims, 7 DrawingFigures mes 99,939, l+l2,+300l l 6 Ps, +F F H a a was Klqm AWLIFIER s1 Im -K n i REF 1: g 67 l soom "5:, 129592.. I r egs, I 1 km AMPUFIER 12oCHANNEL. 2

.CWPUNG TRANSFWE AAA b VOLT AGE '3 FDLLOVER K8 +F-F (+12.+300)YPS| +FHIGH FLQA VOLTAGE my CURRENT SUPPLY AMPLIFIER PATENTEDum 10 I912 SHEET 1BF 5 INVENTOR JOHN F. KLINCHUCH CBZwMAl'DMqMJ ATTORNEY PATENTEU I97? I3.697143 SHEET 2 OF 5 INVENTOR JOHN F KLINCHUCH wmm w f,

ATTORNEY P'ATENTEDum 10 I972 SHEET 5 BF 5 TIMING MATRIX l =CLOSED SWITCHO= OPEN SWITCH T THROUGH T ARE DEFINED IN FIG. 2

FIG.

7 INVENTOR JOHN F. KLINCHUCH (112mm M BACKGROUND OF THE INVENTION Thepresent invention relates to a system for electrostatically supportingan electrically conductive member in space and, more particularly, to africtionless support means for supporting the rotor of a gyroscope usingalternating polarity pulse amplitude signals which are supplied tosupporting electrodes to centrally locate the gyroscope rotor betweenthe electrodes and to provide output signals which indicate thedisplacement of the rotor with respect to the supporting electrodes.

For background information, an electrostatic gyroscope is a free-rotorgyroscope in which sphericalbearing support forces are derived from anelectric field. The rotor is generally an aluminum or beryllium spherewhich may be either solid or hollow. The electrostatic support consistsgenerally of pairs of spherical segment electrodes dispersed about therotor.

Prior known devices for electrically supporting a rotor of a gyroscopeare disclosed, for example, in U. S. Patent Application, Ser. No.50,604, entitled ELEC- TROSTATIC SUPPORT SYSTEM, by J. L. Atkinson. Inthat application there is disclosed an electrostatic gyroscope of theaforementioned type and further including a periodic signal source forproviding a squarewave reference signal with a pair of amplifiersconnected to the electrodes of a pair with each amplifier receiving theperiodic signal as an input. A differential amplifier is connectedacross the pair of electrodes to provide an output signal proportionalto the voltage difference between the electrodes and the supportedconductive member. Switch means are utilized to increase or decrease thegain of one amplifier while decreasing or increasing, respectively, thegain of the other amplifier in response to the difierence signal so asto increase the magnitude of the periodic signal applied to oneelectrode and to decrease the magnitude of the periodic signal appliedto the other electrode so as to help coerce the electrically supportedconductive member towards a centered position.

Other known devices are disclosed, for example, in US. Pat. No.3,098,679, issued July 23, I963, entitled PASSIVE CONTROL CIRCUIT FORELECTRO- STATIC BEARING, by W. F. DeBoice, and U. S. Pat. No. 2,919,583,issued Jan. 5, 1960, entitled MAG- NETICALLY SUPPORTED GYROSCOPE, by H.M. Parker. An additional patent of interest is U. S. Pat. No. 3,338,644,issued Aug. 29, 1967, entitled ELECTRO- STATIC SUPPORT CIRCUIT, by J. L.Atkinson, et al., which patent is assigned to North American RockwellCorporation, the assignee of the present application.

The main problems encountered with prior art systems are the following:

1. Providing a good separation between the signals used to measure rotordisplacement and those used to apply force on the rotor. The suspensionsystem described in this application has been proven by laboratory teststo provide improved separation from the system described in U. S. Pat.No. 3,338,664;

2. the limited g capability of systems similar to those described in U.S. Patent Application, Ser. No. 50,604;

3. the sensitivity of drift rate changes to charge trapped on the rotorfor systems which do not periodically change the polarity of the chargeapplied to each electrode; and

4. providing an accurate determination of force applied to the gyroscoperotor so as to permit the use of the electrostatic gyroscope as anaccelerometer.

The present invention provides an improvement in each of these areasover prior art systems. In addition, applicants alternating polaritycharge system reduces the drift rate between rotor lift-offs from 3 perhour to 0.03 per hour.

SUMMARY OF THE INVENTION According to one aspect of the invention, thereis provided an electrostatically supported gyroscope in which aconductive ball is supported between pairs of electrodes and asuspension system which utilizes a plurality of difference amplifiersfor sensing the voltage difference between electrodes of a pair.Connected to receive the outputs of the difference amplifiers are sampleand hold means which sample the output of the difference amplifiers eachpositive and negative period of the difierence signal and store thesamples. Difference means are used to invert one sample of the storedsignal and to add the inverted sample to the noninverted sample. Thesummed signal from the difference means is proportional to thedisplacement of the ball with respect to an electrode pair. The displacement signal is then servo-compensated and fed to a charge means throughswitching means to apply a charge to the electrodes in a direction andwith a force adequate to restore the ball to a centered position betweenthe electrodes.

It is, therefore, an object of the present invention to provide animproved system for suspension of an electrically conductive ball.

It is another object of the present invention to provide anelectrostatic suspension system for a rotating ball which suspensionsystem minimizes drift rate sensitivity to charges trapped on the rotor.

Another object of the present invention is to provide an improvedalternating pulse amplitude suspension system for an electrostaticgyroscope.

The foregoing objects of the present invention will become more apparentand better understood when taken in conjunction with the followingdescription and accompanying drawings, throughout which like charactersindicate like parts and which drawings form a part of this application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates in a sectioned viewan electrically conductive ball rotor positioned for levitation betweena plurality of electrodes;

FIG. 2 illustrates in an exploded view the positioning and shape of thelevitating electrodes used with the preferred embodiment of theinvention;

FIGS. 3a and 3b which connect end to end illustrate in block diagramform the preferred embodiment of the invention;

FIGS. 4a and 4b are waveforms useful in understanding the operation ofthe preferred embodiment of FIGS. 3a and 3b; and

FIG. 5 is a chart illustrating the switching times of a switching meansused in the preferred embodiment of FIGS. 3a and 3b.

FIGS. 1 and 2 show schematically a gyroscopeicom prised of anon-conductive ceramic case with a spherical interior contour and anelectrically conductive surface ball 11 which may or may not be spun asa rotor to act as a gyroscope. Within the case 10 is a spherical cavity12 lined with eight octantal electrodes, shown as seen from the outside,in FIG. 2, which are denoted for convenience in analysis at +1 1, +2 2,+3 3, and +4 4. Eachpair, e. g., +1 l, are diemetrically opposed. Theelectrode surfaces may be thought of as a projection upon a sphere ofthe eight faces of a regular octahedron. The axes of the electrodes setare then taken as X, Y and Z in FIG. 2. The X and Z axes define theplane along which a section is taken for FIG. 1. A vacuum exists withinthe spherical cavity 12.

Each pair of electrodes, e.g., +1 1, are connected into a suspensionmeans, to be described, such that the departure of the ball 11 from thecenter of the spherical cavity 12, which, for example, decreases the gapat +1 V and increases it at l, resultsin a voltage decrease andincrease, respectively, to center the ball.

Referring now to FIG. 3a, in conjunction with FIG. 3b, and the timingmatrix of FIG. 5, four difference amplifiers, labeled 12a to 12d, areeach connected to a pair of electrodes, +1 1, +2 2, +3 3, and +4 4,respectively. The +1 1 electrodes are pair I. Electrodes +2 2 form pairII with electrodes +3 3 forming pair III and electrodes +4 4 formingpair IV. The output of these difference amplifiers are fed to pairs ofsample and hold means 16a 16b; 16c 16d; 16e 16f; 16g 16h, respectively.One sample and hold means of a pair receives a reference signal r withthe other sample and hold means of the pair receiving the referencesignal r Reference signal r causes sample and hold means 16a, 16c, 16cand 163 to store the difference between the voltages at electrode pairsduring the time period T Reference signal r causes sample and hold means16b, 16d, 16f and 16h to store the difference between electrode pairsduring the time period T FIGS. 4a and 4b illustrate by waveforms thatthe magnitude of the charge applied to the electrodes during the timeperiod T or T is always equal to the pre load charge Q, which is aconstant. The displacement of the rotor 11 within the cavity 12 can beelectrically determined for plate pair 1 and 1 by use of the followingequations:

V voltage at electrode 1;

C, capacitance between the rotor and electrode when the rotor iscentered;

C capacitance between the rotor and electrode 1;

C4 capacitance between the rotor and electrode X 1 displacement of therotor from the cavity center along axis 1;

h nominal gap between the rotor and the electrodes; and

J92 K eonstant 00h Equation (3) shows that the voltage differencebetween opposite electrodes is proportional to rotor displacement X Eachpair of sample and hold means has its output connected to one input ofthe difference amplifiers 17a, 17b, or 17d. The output of the differenceamplifiers are labeled m m m and m.,, respectively. It is necessary tosample the signals at the outputs of difference amplifiers 12 usingpairs of staggered gated sample and hold means in the manner previouslydescribed because the polarity of the difference signal during sampleperiod T is opposite from the polarity of the difference signal duringperiod T The signals from the difference amplifiers 17 are fed to a 4:3signal transformation circuit 19, comprised of summation amplifiers 20a,20b, and 20c. The transformation circuit changes the four input signalsinto signals corresponding to the signals along orthogonal axes X, Y andZ, respectively. The transformation converts four dependent pickoffsignals to a set of three independent signals. This prevents saturationof the suspension electronics when pickoff. offset voltages occur. Thesuspension electronics gain is extremely high at low frequency and verysmall offset voltages will saturate these electronics if the channelsare not independent. A high gain at low frequency is required in orderto maintain the average position of the rotor at the center of thecavity in the presence of gravity forces acting on the rotor. An averagedisplacement of the rotor from the center of the cavity results in driftrate and attitude readout errors. Signals from the summation amplifiers20 are then fed to corresponding notch filters 21a, 21b, and 210,respectively, and from there to servo networks 22a, 22b and 22c,respectively. Each of the servo networks operate to provide servocompensation for the suspension electronics which compensationstabilizes the system according to wellknown servo feedback methods. Thenotch filters provide the necessary filter characteristics for rotorspeed control similar to the type described in US. Patent Application,Ser. No. 77,993, entitled Speed Control, by J. Boltinghouse et al. Theoutput of the servo networks along with the outputs from differenceamplifiers 17a through 17d are fed to summation amplifiers 23a through23d. Summation amplifiers 23a through 23d form a 3:4 signal conversionmeans 24 to reconvert the signals received at the amplifiers inputs backinto the four coordinate systems. The outputs from amplifiers 23athrough 23d are each available in a positive value and a negative valueas a result of being processed through inverting amplifiers 27a through27d. A precision voltage reference 25 provides a constant signal K Q andthe negative value of this constant signal KQp, by means of invertingamplifier 26.

The charges which suspend the ball between the electrodes are applied tothe electrodes by the system shown in FIG. 3. The operation of thecharge channel 1 for electrode +1 will be explained. Electrode +1 isservices through channel 1 with electrode 1 services through channel 2.Each channel is identical in construction and will hereinafter bereferred to as charge channels. The operation of the charge channel forall other electrodes being identical to the operation of the chargechannel for electrode +1.

The charge applied to channel 1 is proportional to the voltage appliedto amplifier 38. The input voltage to amplifier 38 is controlled byapplying voltages K, 0,, K, O," K, Q,,, and -I(, Q through switches 31,32, 33, 34, 35 and 36. The opening and closing times of these switchesappear in FIG. 5 in the tinting matrix diagram. The output signal fromamplifier 38 is fed to a coupling transformer 50. The couplingtransformer operates to isolate the low level signal from amplifier 38from the high voltage potentials that are applied to the electrodes. Thesecondary of transformer 50 is connected at one terminal to the input ofamplifier 52. The other transformer secondary terminal :is connected tothe junction of resistor 67, capacitor 66, and the input to a floatingpower supply 64. The secondary of the coupling transformer applies avoltage, V with respect to floating ground, F to amplifier 52.This'amplifier will cause the high voltage amplifier 61 to drive acurrent through capacitor 66 until the voltage V across the capacitor 66equals V The voltage follower 62 is a very high input impedanceamplifier. Therefore, all current passing through capacitor 66 isapplied to electrode +1 except for the small leakage current throughresistor 68. Thus, the amplifier 52 serves to control the charge appliedto the electrode, since the charge on electrode +1 is equal to thecharge on capacitor 66. When the rotor 11 is centered, the time constantof capacitor 66 and resistor 67 is identical to the time constant of theelectrode capacitance and resistor 68. For this condition, the leakagethrough resistor 68 is compensated for by the leakage through resistor67, giving a net leakage of zero current to the electrode. Resistor 68is necessary to prevent charge accumulation errors due to minute leakagecurrents which may exist. The floating power supply furnishes power tothe voltage follower 62 and amplifier 52. This allows the use of lowpower, low voltage, high bandwidth integrated circuits. The groundreference for these devices is, F,,, which follows the electrodepotential.

No charge is applied to the electrodes during time periods T, and T Thisis to allow the, high voltage power supplies, which drive the highvoltage current amplifier 61 to change state. When electrode +1 has apositive polarity of preload charge, Q applied, the high voltagesupplies have +300 .VDC applied to P8,, and l 2 VDC applied to PS Whenthe electrode has a negative polarity of preload charge, Q,,, applied,the high voltage supplies have +12 VDC applied to PS, and 300 VDCapplied to PS Switching the high voltage supplies in this manner reducesthe sustaining voltage requirements for the transistors used in the highvoltage current amplifier 61.

FIG. 4a illustrates the waveform present on electrode +1 for onecomplete cycle, while FIG. 4b illustrates the waveform present onelectrode -1 for one complete cycle.

The times, T, are set forth, for the preferred embodiment, as follows:

T, 5 microseconds T 15 microseconds T 10 microseconds T, microseconds T5 microseconds T 15 microseconds T 10 microseconds T 20 microseconds T100 microseconds I Y The preload charges for electrode pairs 1 and IIIare in time phase and are out of phase with the preload charges forelectrode pairs II and IV.

The net force exerted on the rotor along an axis extending from thecenter of the cavity 12 through the center of electrode +1 isproportional to the amplitude of, K, Q.,. The periods in which a netforce is exerted on the rotor are T T T and T as shown in FIGS. 4a and4b. The force produced by electrode +1 along its central axis duringperiods T T.,, T, and T, is described by the following equations:

where I F,,, net force along electrode +1 axis; F, =force applied byelectrode 1;

F force applied by electrode 1;

K, constant relating charge to force;

Q, preload charge which is a constant; and

Q variable charge proportional to K, Q,

Equation (7) shows that the force produced along the center axis ofelectrode +1 is proportional to the servo command signal, K, (,2

In summary, by applying alternating polarity pulse amplitude signals tothe electrodes of an electrostatically supported conductive rotor, it ispossible to minimize the charges trapped on the conductive rotor,thereby increasing the accuracy with which the rotors position withrespect to the electrodes is determined.

While there has been shown what is considered to be the preferredembodiment of the present invention, it will be manifest that manychanges and modifications may be made therein without departing from theessential spirit of the invention. It is intended, therefore, in theannexed claims, to cover all such changes and modifications asfallwithin the true scope of the invention.

I claim:

1. A suspension system for an electrostatic gyroscope of the type whichincorporates pairs of electrodes arranged in a symmetrical array arounda conductive ball, which ball is adapted to be spun about a=spin axis,and wherein said suspension system is comprised of:

a plurality of difference amplifier means for sensing the voltagedifference between electrodes of a pair and said conductive ball andproviding a. signal proportional to the voltage difference;

sample and hold means for sampling the output of the differenceamplifier each positive and negative period of the difference signal andfor holding said samples;

difference means for inverting one sample of said held signal and forsumming the inverted sample with the non-inverted signal to provide asignal proportional to the displacement of the ball with respect to theelectrode pair;

BEST AVAILABLE COPY means for receiving the output signals from saiddifference means and for applying servomechanism compensation to saidsignals;

charge means for alternately applying potentials to the electrodes of apair in response to a control signal; a i

a source of constant amplitude alternate polarity signals; and i switchmeans for receiving the signals from said difference means and forperiodically providing said signals to said charge means as said controlsignal and, in addition, for periodically connecting the input of saidcharge means to said constant alternate polarity signals so as to removecharge build-ups from said conductive ball.

2. The system according to claim 1 wherein said switch means alsoperiodically connects the input of said charge means to a referencepotential.

3. A suspension system for an electrostatic gyroscope of the type whichincorporates pairs of electrodes arranged in a symmetrical array arounda conductive ball, which ball is adapted to be spun about a spin axis,and wherein said suspension system is comprised of:-

means for sensing the voltage difierence between electrodes of a pairand said conductive ball and for providing a signal proportional. tothis difference;

means for digitally comparing the difference between positive andnegative periods of said difference signal to provide a displacementsignal;

charge means for selectively applying potentials to the electrodes of apair in response to control signals;

control means responsive to said displacement signal for applying acontrol signal to said electrodes in alternating polarity to positionthe conductive ball so as to minimize said displacement signal;

a source of constant amplitude alternate polarity signals; and

means for periodically connecting said control means to said source ofconstant amplitude alternating polarity signals so as to apply saidconstant amplitude signal to said electrodes so as to diminish thecharge accumulation on said conductive ball.

4. The suspension system according to claim 1 wherein said charge meansis comprised of:

a floating power supply having an output and an input, the output levelof which varies in accordance with the potential applied at its input;

amplifier means powered by said floating power supply for receiving theservomechanism compensated output signals, said amplifier means amplify-LII ing said compensated signal;

"a current amplifier means for receiving the signal from said amplifiermeans and for providing said amplified signal in the form of a potentialto the input of said floating power supply;

a voltage follower means powered by said floating power supply havingits input connected to the electrode side of said capacitor means andits output connected to an input of said amplifier means so as to feedback to said amplifier means the potential in said electrode; and

resistor means connected across said capacitor means and to a refere cepotential. 5. A suspension system or an electrostatic gyroscope of thetype which incorporates pairs of electrodes arranged in a symmetricalarray around a conductive ball, which ball is adapted to be spun about aspin axis, and wherein said suspension system is comprised of:

a plurality of difference amplifier means for sensing the voltagedifference between electrodes of a pair and said conductive ball, andproviding a signal proportional to said voltage difference;

a plurality of sample and hold means, one connected to the output ofeach difference of said difference amplifier each positive and negativeperiod of the difference signal and for holding said samples;

difference means for providing a displacement signal which is the sum ofthe positive and negative periods of the difference signal fromsaidsample and hold means indicating the displacement of the conductive ballbetween the pair of electrodes;

signal transformation means for receiving the displacement signals fromsaid displacement means and for transforming said displacement signalsinto signals corresponding to the displacement of said conductive ballalong three mutually orthogonal axes;

servomechanism compensation means for compensating said displacementsignals so as to remove undesired portions of said signals;

charge means for alternately applying potentials to the electrodes of apair in response to a control signal;

a source of constant amplitude alternate polarity signals; and

switch means for receiving the signals from said difference means andfor periodically providing said signals to said charge means as saidcontrol signal and, in addition, for periodically connecting the inputof said charge means to said constant alternate polarity signals so asto remove charge build-ups from said conductive ball.

a a: n:

1. A suspension system for an electrostatic gyroscope of the type whichincorporates pairs of electrodes arranged in a symmetrical array arounda conductive ball, which ball is adapted to be spun about a spin axis,and wherein said suspension system is comprised of: a plurality ofdifference amplifier means for sensing the voltage difference betweenelectrodes of a pair and said conductive ball and providing a signalproportional to the voltage difference; sample and hold means forsampling the output of the difference amplifier each positive andnegative period of the difference signal and for holding said samples;difference means for inverting one sample of said held signal and forsumming the inverted sample with the non-inverted signal to provide asignal proportional to the displacement of the ball with respect to theelectrode pair; means for receiving the output signals from saiddifference means and for applying servomechanism compensation to saidsignals; charge means for alternately applying potentials to theelectrodes of a pair in response to a control signal; a source ofconstant amplitude alternate polarity signals; and switch means forreceiving the signals from said difference means and for periodicallyproviding said signals to said charge means as said control signal and,in addition, for periodically connecting the input of said charge meansto said constant alternate polarity signals so as to remove chargebuild-ups from said conductive ball.
 2. The system according to claim 1wherein said switch means also periodically connects the input of saidcharge means to a reference potential.
 3. A suspension system for anelectrostatic gyroscope of the type which incorporates pairs ofelectrodes arranged in a symmetrical array around a conductive ball,which ball is adapted to be spun about a spin axis, and wherein saidsuspension system is comprised of: means for sensing the voltagedifference between electrodes of a pair and said conductive ball and forproviding a signal proportional to this difference; means for digitallycomparing the difference between positive and negative periods of saiddifference signal to provide a displacement signal; charge means forselectively applying potentials to the electrodes of a pair in responseto control signals; control means responsive to said displacement signalfor applying a control signal to said electrodes in alternating polarityto position the conductive ball so as to minimize said displacementsignal; a source of constant amplitude alternate polarity signals; andmeans for periodically connecting said control means to said source ofconstant amplitude alternating polarity signals so as to apply saidconstant amplitude signal to said electrodes so as to diminish thecharge accumulation on said conductive ball.
 4. The suspension systemaccording to claim 1 wherein said charge means is comprised of: afloating power supply having an output and an input, the output level ofwhich varies in accordance with the potential applied at its input;amplifier means powered by said floating power supply for receiving theservomechanism compensated output signals, said amplifier meansamplifying said compensated signal; a current amplifier means forreceiving the signal from said amplifier means and for providing saidamplified signal in the form of a potential to the input of saidfloating power supply; a voltage follower means powered by said floatingpower supply having its input connected to the electrode side of saidcapacitor means and its output connected to an input of said amplifiermeans so as to feed back to said amplifier means the potential in saidelectrode; and resistor means connected across said capacitor means andto a reference potential.
 5. A suspension system for an electrostaticgyroscope of the type which incorporates pairs of electrodes arranged ina symmetrical array around a conductive ball, which ball is adapted tobe spun about a spin axis, and wherein said suspension system iscomprised of: a plurality of difference amplifier means for sensing thevoltage difference between electrodes of a pair and said conductiveball, and providing a signal proportional to said voltage difference; aplurality of sample and hold means, one connected to the output of eachdifference of said difference amplifier each positive and negativeperiod of the difference signal and for holding said samples; differencemeans for providing a displacement signal which is the sum of thepositive and negative periods of the difference signal from said sampleand hold means indicating the displacement of the conductive ballbetween the pair of electrodes; signal transformation means forreceiving the displacement signals from said displacement means and fortransforming said displacement signals into signals corresponding to thedisplacement of said conductive ball along three mutually orthogonalaxes; servomechanism compensation means for compensating saiddisplacement signals so as to remove undesired portions of said signals;charge means for alternately applying potentials to the electrodes of apair in response to a control signal; a source of constant amplitudealternate polarity signals; and switch means for receiving the signalsfrom said difference means and for periodically providing said signalsto said charge means as said control signal and, in addition, forperiodically connecting the input of said charge means to said constantalternate polarity signals so as to remove charge build-ups from saidconductive ball.